Systems for controlling the flow of fluids, such as compressed air, natural gas, oil, propane, or the like, are generally known in the art. These systems often include at least one control valve for controlling various flow parameters of the fluid. Typical control valves include a control element such as a valve plug, for example, movably disposed within the flow path for controlling the flow of the fluid. The position of such a control element can be controlled by a positioner via a pneumatic actuator such as a piston actuator or a diaphragm-based actuator, as is known in the art. Conventional positioners deliver pneumatic signals via supply fluid to the actuator to stroke the control element of the control valve between an open and closed position, for example. The speed at which a the control valve can stroke partly depends on the size of the actuator and the flow of supply fluid contained in the pneumatic signal. For example, larger actuators/control valves typically take longer to be stroked when a positioner of equal flow output is used.
Therefore, such systems additionally employ one or more volume boosters located between the positioner and the actuator. The volume boosters are used to amplify the volume of supply fluid in relation to the pneumatic signal sent from the positioner, thereby increasing the speed at which the actuator strokes the control element of the control valve. Specifically, it should be understood by one of ordinary skill in the art that the volume booster is connected between the fluid supply and the valve actuator. Employing a pneumatic restriction in the volume booster allows large input signal changes to register on the booster input diaphragm sooner than in the actuator. A large, sudden change in the input signal causes a pressure differential to exist between the input signal and the output of the booster. When this occurs, the booster diaphragm moves to open either a supply port or an exhaust port, whichever action is required to reduce the pressure differential. The port remains open until the difference between the booster input and output pressures returns to within predetermined limits of the booster. A booster adjustment device may be set to provide for stable operation; (i.e. signals having small magnitude and rate changes pass through the volume booster and into the actuator without initiating booster operation).
However, conventional booster designs are susceptible to flow induced noise. It is generally known that highly velocity fluid streams generate noise resulting from jet or other highly concentrated fluid stream interaction flowing through a conduit or exiting an orifice. Noise attenuators may be affixed to such devices to substantially reduce such generated noise. However, such noise attenuators are typically located adjacent to and immediately downstream of exit point for the fluid. Such a mounting configuration may be disadvantageous. For example, locating the noise attenuator downstream from the volume booster may induce a pressure reversal across a diaphragm assembly substantially limiting the lifespan of the diaphragm assembly. Additionally, downstream from the noise exit port where pressure differentials are greatest, and therefore fluid velocities are the highest, jet recombination may occur leading to greater sound pressure levels (i.e. more intense or louder noise).